Typical values of z-resolution for different Digital Breast Tomosynthesis systems evaluated in a multicenter study

PURPOSE

The aim of the present study, conducted by a working group of the Italian Association of Medical Physics (AIFM), was to define typical z-resolution values for different digital breast tomosynthesis (DBT) models to be used as a reference for quality control (QC). Currently, there are no typical values published in internationally agreed QC protocols.

METHODS

To characterize the z-resolution of the DBT models, the full width at half maximum (FWHM) of the artifact spread function (ASF), a technical parameter that quantifies the signal intensity of a detail along reconstructed planes, was analyzed. Five different commercial phantoms, CIRS Model 011, CIRS Model 015, Modular DBT phantom, Pixmam 3-D, and Tomophan, were evaluated on reconstructed DBT images and 82 DBT systems (6 vendors, 9 models) in use at 39 centers in Italy were involved.

RESULTS

The ASF was found to be dependent on the detail size, the DBT angular acquisition range, the reconstruction algorithm and applied image processing. In particular, a progressively greater signal spread was observed as the detail size increased and the acquisition angle decreased. However, a clear correlation between signal spread and angular range width was not observed due to the different signal reconstruction and image processing strategies implemented in the algorithms developed by the vendors studied.

CONCLUSIONS

The analysis led to the identification of typical z-resolution values for different DBT model-phantom configurations that could be used as a reference during a QC program.

ASSESSMENT OF PCXMC MONTE CARLO SIMULATIONS IN SLOT-SCANNING-BASED EXAMINATIONS: COMPARISON WITH IN-PHANTOM THERMOLUMINESCENT DOSIMETRY

Slot-scanning technology is nowadays a valid solution for the follow-up of chronic musculoskeletal disorders on children and adolescent patients, but there is no commercial software designed for simulating this X-ray beam geometry. PC Program for X-ray Monte Carlo (PCXMC) is a widespread Monte Carlo software developed for dose computation in projection radiography. In this study, experimental measurements were performed to evaluate its applicability in examinations with a slit-beam device. Physical phantoms corresponding to an adult and a 5-y-old child with calibrated thermoluminescent dosemeters were used for experiments. Different simulation approaches were investigated. Differences between measured and calculated organ doses ranged from -95 to 67% and were statistically significant for almost all organs. For both patients, PCXMC underestimated the effective dose of about 25%. This study suggests that PCXMC is not suited for organ dose evaluation in examinations with slot-scanning devices. It is still a useful tool for effective dose estimation when a proper correction factor is applied.

Flat Panel Angiography in the Cross-Sectional Imaging of the Temporal Bone: Assessment of Image Quality and Radiation Dose Compared with a 64-Section Multisection CT Scanner

BACKGROUND AND PURPOSE

Cross-sectional imaging of the temporal bone is challenging because of the complexity and small dimensions of the anatomic structures. We evaluated the role of flat panel angiography in the cross-sectional imaging of the temporal bone by comparing its image quality and radiation dose with a 64-section multisection CT scanner.

MATERIALS AND METHODS

We retrospectively collected 29 multisection CT and 29 flat panel angiography images of normal whole-head temporal bones. Image quality was assessed by 2 neuroradiologists, who rated the visualization of 30 anatomic structures with a 3-point ordinal scale. The radiation dose was assessed with an anthropomorphic phantom.

RESULTS

Flat panel angiography showed better image quality than multisection CT in depicting the anterior and posterior crura of the stapes, the footplate of the stapes, the stapedius muscle, and the anterior ligament of the malleus (P < .05). In contrast, multisection CT showed better image quality than flat panel angiography in assessing the tympanic membrane, the bone marrow of the malleus and incus, the tendon of the tensor tympani, the interscalar septum, and the modiolus of the cochlea (P < .05). Flat panel angiography had a significantly higher overall image quality rating than multisection CT (P = .035). A reduction of the effective dose of approximately 40% was demonstrated for flat panel angiography compared with multisection CT.

CONCLUSIONS

Flat panel angiography shows strengths and weaknesses compared with multisection CT. It is more susceptible to artifacts, but due to the higher spatial resolution, it shows equal or higher image quality in assessing some bony structures of diagnostic interest. The lower radiation dose is an additional advantage of flat panel angiography.

[Non-palpable lesions of the breast. Retrospective analysis of mammographic and ultrasonographic indications for surgery]

INTRODUCTION

The differential diagnosis of malignancy in small foci of microcalcifications or in extremely small nodes can be difficult. We carried out a retrospective analysis of integrated mammographic and US results, correlated with histologic data, to assess the limitations of each method and to optimize and benign/malignant ratio.

MATERIALS AND METHODS

Our series consisted of 485 nonpalpable breast lesions submitted to histologic examination after vegetable charcoal marking. We gave each lesion an 0-5 score according to the degree of diagnostic doubt/suspicion after mammography and US, which results were correlated with histologic data to assess the carcinoma frequency in the various groups identified.

RESULTS

The analysis of mammographic and US images showed that the most frequent mammographic alteration in the lesions submitted to biopsy was an isolated cluster of microcalcifications (40.99%): of these, 36.86% were neoplastic. The nodules submitted to biopsy, which were 29.81% of the total, showed a cancer rate (36.80%) very similar to that of the microcalcifications. The carcinoma rate rose to 37.93% when the microcalcifications were associated with nodes. The highest carcinoma rates, i.e., 52.94% and 66.66%, respectively, were found in parenchymal distortions, either isolated or associated with microcalcifications, which however were only 7.03% and 3.10%, respectively, of the total number of cases.

DISCUSSION AND CONCLUSIONS

Our study showed that: 1) a highly suspicious US result must be seriously considered when a negative mammography has poor intrinsic contrast; 2) a highly suspicious US image with a little suspicious good contrast mammography requires further confirmation before surgery is planned; 3) when the mammographic finding is mid-to-highly suspicious, further investigations are needed even if US is negative. To conclude, even though the histologic examination of nonpalpable breast lesions involves performing a biopsy, we believe this is acceptable when performed on an outpatient basis, under local anesthesia and removing a limited amount of tissue only. The benign/malignant ratio ranges 2 to 1.5: if it is further reduced (below 1.5), there will be the risk of missing some early neoplastic lesions.

[The doses absorbed by the patients and the exposure of the operators in dental radiodiagnosis]

The present paper reports an updated dosimetry of dental radiology since it presents the data relative to 7 radiological techniques. The doses to 9 organs were measured on a Randoman phantom using TLD (4 in each chosen cavity) for lenses, tongue, cervical vertebrae (C2), thyroid, ovaries, uterus and testes. The examinations were subsequently repeated after applying X-ray shields to the phantom. The main conclusions follow: a) local doses are never negligible but can be really high, especially for tongue (1.880 mGy), thyroid (1.011 mGy), and C2 (0.699 mGy); b) X-ray shields for lenses, ovaries, uterus and testes have proven to be unnecessary; in a more general context, X-ray shields should be evaluated by the Health Physics Dept., especially relative to radiation leaks from the X-ray tube. As for the thyroid, X-ray shields have proven very useful but can result in repeated acquisitions because of possible interference with the radiological image; c) technicians' risk, in the present experimental conditions, does not exceed the threshold values recommended by Italian laws. At any rate, the use of fixed or mobile shieldings should always be evaluated while keeping in mind the specific working conditions in radiology departments.

[Sources of ionizing radiation in dwellings]

According to recent surveys made by the International Commission on Radiological Protection (ICRP) and the World Health Organization (WHO), it has been estimated that in temperate regions people spend only 20% of their time outdoors and spend the remaining 80% indoors (homes, schools, other buildings). It is therefore important to establish whether radiation sources exist inside buildings in order to assess risk for the population. The 238U and 232Th radioactive chains are of particular importance because of Radon and Radon daughter production and 40K as component of building materials. It has been estimated that about 4.5% of lung cancers observed in the population are associated with exposure to Radon daughters. In order to comply with international regulations it is estimated that 1.5% of the existing dwellings in temperate regions need to be improved.

[NIOBI-X filter: reduction of patient exposure and effect on image quality]

Patient protection against ionizing radiation has become more and more important and the subject has been included in all the latest ICRP publications. Recently a 50 microns Niobium filter (NIOBI-X) has come out, which, installed on tungsten anode X-ray apparatuses, allows patient dose reduction by absorbing the radiation which does not contribute to the image. In order to verify the NIOBI-X actual effect on image quality and on patient dose reduction, image resolution, image contrast and patient exposure (air-Kerma) were measured using a bone-equivalent stepped wedge. The NIOBI-X, added to the total filtration of the X-ray apparatus, allows an air-Kerma reduction of about 50% from 60 to 130 kV. In the case of bone-equivalent material exposure the filter causes a slight contrast loss and does not affect, or even improves, image resolution. Before choosing the NIOBI-X filter for all the X-ray apparatuses a cost-benefit analysis should of course be made by evaluating results and cost related to other kinds of filter. With particular regard to Aluminium filters, whose prices are far lower than Niobium ones, it has to be pointed out that: 1) in order to have the same air-Kerma reduction the Aluminium filter thickness must be quite heavy (2.8 mm) which causes practical problems of use; 2) the Aluminium filter causes image quality loss especially at lower kVs.